Adjustment of Background Scanning Interval Based on Network Usage

ABSTRACT

In a Wireless Local Area Network (WLAN), roaming from one access point to another by a mobile station without interruption to network service may be facilitated by frequently performing background scans to find neighboring access points while the mobile station is associated to the WLAN. Frequent background scanning, however, depletes battery life. By dynamically adjusting the background scanning interval during the mobile station&#39;s association to the WLAN, the mobile station&#39;s immediate need for network connectivity performance may be met, while simultaneously prolonging battery life. For example, by using a shorter background scanning interval during a telephone conversation, network connectivity performance may be maintained throughout the call. Longer background scanning intervals may be used during periods when interruptions to network connectivity may be better tolerated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/383,233 filed May 15, 2006, entitled “Adjustment of BackgroundScanning Interval Based on Network Usage”, which is incorporated byreference in its entirety.

BACKGROUND

In a Wireless Local Area Network (WLAN) comprising a number of accesspoints (APs), mobile stations (STAs) roam from one AP to another as theychange locations with their users. There are two ways for a mobilestation to discover available access points to roam to. Either it cansearch periodically for alternatives, so that it has a list ready whenit is ready to roam, or it can wait until it is necessary to roam tosearch for other access points. In the first approach, calledpre-emptive discovery, a station periodically scans the WLAN channels tolearn about its neighboring access points, in a process usually referredto as background scanning. This process may be either active, where thestation sends probes out on all its channels to detect neighboringaccess points, or passive, where the station listens on all its channelsfor access point beacons. The frequency of background scans directlyimpacts the roaming performance of a WLAN device. If background scansare not performed frequently enough, the device may fail to pick theoptimal access point while roaming, or even fail to find a neighbor anddisconnect.

Decreasing the background scanning interval improves networkconnectivity performance; however, it also degrades battery life,because scanning is a process that consumes a significant amount ofpower. In selecting a scanning interval, a compromise is made betweenpreserving battery power, and providing adequate roaming capabilities.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example and not limitation in thefigures of the accompanying drawings, in which like reference numeralsindicate corresponding, analogous or similar elements, and in which:

FIG. 1 is an illustration of an exemplary deployment of a wireless localarea network (WLAN) in a building, according to an embodiment of theinvention. The WLAN includes access points (APs) and a switched, routedfabric including a server;

FIG. 2 is a flowchart of an exemplary method implemented by a mobilestation to conserve battery power while roaming, according to anembodiment of the invention; and

FIG. 3 is a block diagram of an exemplary mobile station compatible withthe method shown in FIG. 2.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of embodiments.However it will be understood by those of ordinary skill in the art thatthe embodiments may be practiced without these specific details. Inother instances, well-known methods, procedures, components and circuitshave not been described in detail so as not to obscure the embodiments.

While decreasing the background scanning interval improves seamlessroaming capabilities, it degrades battery life, since scanning is aprocess that consumes a significant amount of power. It is necessary,therefore, to trade off network connectivity performance against batteryconservation. Typically, the background scanning interval for a STA isset to a constant value by the device manufacturer. However, using asingle background scanning interval that stays constant over time maynot be ideal. The need for network connectivity performance is notconstant over time, but rather, varies with how the STA is being usedwith respect to its network connection.

A mobile station that may be used with a WLAN may support various typesof network-related activity. For example, the mobile station may beequipped for any of the following activities or any combination thereof:Internet browsing, sending and receiving e-mail, conducting VoIPconversations, and the like. These activities have different needs fornetwork connectivity. A VoIP application, for example, has a significantneed for uninterrupted network connectivity during an active call.

Different network usage modes may be defined for a STA according to theactivities' needs for uninterrupted WLAN access and bandwidth. The usagemodes may be defined based on: (A) which applications are currentlyactive (i.e., which applications are actively consuming CPU time, or arein the foreground of the STA's screen), (B) how the applications arebeing used with respect to network connectivity, or (C) through directmonitoring of the STA's network traffic.

A non-exhaustive list, Set A, of exemplary network usage modes based onapplications includes:

Disconnected: STA is not connected to the WLAN;

Connected Idle: STA is connected to the WLAN, but the only networkactivity of the STA is that which is required to maintain a connectionto the WLAN;

Connected with User Interface Activity: STA is connected to the WLAN andan application or applications that do not require a network connectionare active, e.g., calculator, task list, calendar, address book etc.;

Connected Email: STA is connected to the WLAN, and an email applicationin the STA is active (e.g. the user is actively typing, reading,sending, and/or receiving email);

Connected Instant Messaging: STA is connected to the WLAN and an instantmessaging application in the STA is active (e.g., the user is activelytyping, reading, sending and/or receiving instant messages);

Connected Browsing: STA is connected to the WLAN and a network browsingapplication in the STA is active;

Connected Media Streaming: STA is connected to the WLAN and a mediastreaming application in the STA is active;

Connected in a Phonecall: STA is connected to the WLAN and a telephoneapplication in the STA is active and a call is established via thenetwork (e.g. a VoIP call).

This list of usage modes is in order of increasing network connectivityperformance requirements, i.e., the network connectivity performancerequirements of a phone call are higher than for instant messaging oremail activities. For activities which have higher requirements fornetwork usage, roaming performance is considered more critical, and ashorter background scanning interval is preferred. In the “Connected ina Phone Call” mode, roaming performance is preferred over powerconsumption, so the background scanning interval may be reduced. In the“Connected Idle” mode, the power consumption becomes more important thanthe roaming performance, and the background scanning interval may beincreased. In the “Disconnected” mode, background scanning is turned off(i.e. the background scanning interval is infinite). For intermediatenetwork usage modes, such as email or instant messaging applications,roaming performance and power conservation may have similar weight, andthe background scan interval may be set at a median level. Other networkusage modes may be defined and included in such a list where appropriateaccording to their anticipated network connectivity performancerequirements.

A non-exhaustive list, Set B, of example network usage modes based onhow the applications are being used with respect to network connectivityincludes:

Disconnected: STA is not connected to the WLAN;

Connected Idle: STA is connected to the WLAN, but the only networkactivity of the STA is that which is required to maintain a connectionto the WLAN. There is either no user interface activity, or there isuser interface activity that is not likely to result in the need totransmit or receive data to/from the network, e.g. calculator, tasklist, calendar;

Connected with User Interface Activity: STA is connected to the WLAN andthere is user interface activity that is likely to result in networkactivity, e.g., looking up a contact in an address book, composing anemail. No network transmission or reception is taking place;

Connected Email: STA is connected to the WLAN, and email is being sentand/or received via the WLAN;

Connected Instant Messaging: STA is connected to the WLAN and the useris actively typing, reading, sending and/or receiving instant messages,so that instant messages and/or notifications about instant messageactivities and statuses are being sent and/or received via the WLAN;

Connected Browsing: STA is connected to the WLAN and a network browsingapplication in the STA is active;

Connected Media Streaming: STA is connected to the WLAN, a mediastreaming application in the STA is active and an audio and/or videostreaming session (e.g. podcast) is in progress;

Connected in a Phonecall: STA is connected to the WLAN and a telephoneapplication in the STA is active and a call is established via thenetwork (e.g. a VoIP call).

This list of usage modes is also in order of increasing networkconnectivity performance requirements. Usage modes having higher networkconnectivity performance requirements may be associated with shorterbackground scanning intervals. Other network usage modes may be definedand included in such a list where appropriate according to theiranticipated network connectivity performance requirements.

In this method, each application may periodically or occasionally sendinformation about the user's activities to a centralized network usageapplication. The network usage application may then determine which ofthe usage modes is appropriate, and may determine a minimal backgroundscanning interval from the usage mode.

It may also be possible to determine the requirements for networkconnectivity performance of the STA by monitoring the actual networktraffic characteristics and deducing the current applications status. Anon-exhaustive list, Set C, of exemplary network usage modes based onnetwork traffic includes:

Disconnected: STA is not connected to the WLAN;

Connected Idle: STA is connected to the WLAN, with sporadic,intermittent network activity (for example, usually 3 frames or less perIEEE 802.11 beacon);

Connected Email: STA is connected to the WLAN, with medium-sized packets(e.g., packets between 200-600 bytes in length), sent within apre-defined packet rate (e.g., at least 10 packets in 20 seconds);

Connected Instant Messaging: STA is connected to the WLAN, with small(e.g., less than 200 bytes in length) intermittent packets from/to thesame destination with inter-packet spacing of approximately one to fiveseconds;

Connected Browsing: STA is connected to the WLAN, and medium to large(e.g., 600-1500 bytes in length) packets are being continuouslytransmitted and received for longer than a few seconds;

Connected Phonecall and/or Media Streaming: STA is connected to theWLAN, and there are periodic incoming and/or outgoing medium-sizehigh-priority packets with inter-packet spacing of less than 100 ms.

In addition, it is possible to combine, either wholly or partially, setsA to C in order to determine the network connectivity requirements ofthe STA. For example, using set A, a STA may have an email applicationthat is currently in the foreground, resulting in the selection of the“Connected e-mail” mode, whereas using set C, monitoring the trafficdirectly determines that the STA's mode is “Connected Idle”. To selectthe most appropriate background scanning interval, a rule may be definedsuch that the mode that corresponds to the shorter background scanninginterval will be selected.

To better balance the requirements of roaming performance and batteryconservation, the background scanning interval may be changeddynamically according to the current network usage mode of the STA. Thismay be done automatically, without any need for user intervention. TheSTA itself may monitor the user's activities and adjust the backgroundscanning interval according to the current WLAN requirements. In oneexample, network usage modes such as defined above may be used tocharacterize the STA's current network needs, and the backgroundscanning interval may be adjusted on the basis of the current networkusage mode. The background scanning may be active or passive or anycombination thereof.

FIG. 1 is an illustration of an exemplary deployment of a wireless localarea network (WLAN) in a building, according to an embodiment of theinvention. The WLAN includes APs 102, 103, 104 and 105 in a switched,routed fabric including a server 106.

A mobile station 110 may be active in the WLAN. A non-exhaustive list ofexamples for mobile station 110 includes a wireless-enabled laptop, awireless-enabled cellphone, a wireless-enabled PDA, a wireless-enabledsmartphone, a wireless-enabled video camera, a wireless-enabled gamingconsole, a wireless Voice over Internet Protocol (VoIP) phone and anyother suitable wireless-enabled mobile station.

In the example of FIG. 1, APs 102, 103, 104 and 105, server 106 andmobile station 110 are compatible with a wireless networking standard,such as the Institute of Electrical and Electronic Engineers (IEEE)802.11 standard for Wireless LAN Medium Access Control (MAC) andPhysical layer (PHY) specifications. However, it will be obvious tothose of ordinary skill in the art how to modify the following for otherexisting WLAN standards or future related standards.

Mobile station 110 may roam, for example, from the coverage area of AP102, to the coverage area of AP 103 during a single conversation. Tomaintain the quality of the conversation, the roaming must happenseamlessly and must be transparent to the user of the station. During aconversation, then, a shorter background scanning interval is desirablein order to maintain at all times a current list of available APs. Onother occasions, when mobile station 110 is not currently in use for aconversation or another activity requiring continuous data streaming, ashort interruption to service may not be noticeable to the user. Duringthese times, a longer background scanning interval may be used toconserve battery power.

FIG. 2 is a flowchart of a method implemented by a mobile station 110,according to an embodiment of the invention. At 202, mobile station 110monitors its own network usage. This may be accomplished either at theSTA application level by monitoring the user's activities, or at a lowerlevel by directly monitoring the STA's own network traffic, or by somecombination of these approaches. For example, separate applications thatare being run on the STA, including for example, an email application,and/or a VoIP application, may send alerts about the user's activitiesto a network usage application. A network usage application may classifythe current state of the STA according to a list of network usage modes,by monitoring which applications are active, or by using the alertmessages from the other applications. Alternatively or additionally, thestation may deduce directly from the characteristics of the networktraffic which of the list of network usage modes reflects its currentstate. For example, medium to large sized packets back-to-back arecharacteristic of a browsing session, medium-sized, high-prioritypackets at a constant rate are characteristic of a telephone VoIP call,and e-mail may have similar characteristics to browsing, but with lessdata and in shorter periods of time. The station may then determine itsimmediate requirement for network connectivity performance from theusage mode.

The usage mode represents the station's immediate requirement fornetwork connectivity performance. At 204, a background scanning intervalis determined on the basis of the station's immediate requirement fornetwork connectivity performance. At 206, the background scanninginterval may be adjusted at the WLAN control level to the intervaldetermined at 204.

Computer-executable instructions for implementing a power managementscheme such as the above-described method in a mobile station may bestored on a form of computer readable media. Computer readable mediaincludes volatile and nonvolatile, removable and non-removable mediaimplemented in any method or technology for storage of information suchas computer readable instructions, data structures, program modules orother data. Computer readable media includes, but is not limited to,random access memory (RAM), read-only memory (ROM), electricallyerasable programmable ROM (EEPROM), flash memory or other memorytechnology, compact disk ROM (CD-ROM), digital versatile disks (DVD) orother optical storage, magnetic cassettes, magnetic tape, magnetic diskstorage or other magnetic storage devices, or any other medium which canbe used to store the desired instructions and which can be accessed byinternet or other computer network forms of access.

FIG. 3 is a block diagram of an exemplary mobile station, according tosome embodiments of the invention. Mobile station 110 includes at leastone antenna 300 coupled to a radio 302, which in turn is coupled to aWLAN controller 304. WLAN controller 304 may be coupled to a memory 306storing firmware 308 to be executed by WLAN controller 304. Mobilestation 110 includes a processor 310 and a memory 312 coupled toprocessor 310. Memory 312 may store executable application code modules314 to be executed by processor 310. Application code modules 314, whenexecuted by processor 310, may perform network functions such asinternet browsing, email, or telephony applications. Memory 312 maystore a network usage application code module 315, which when executedby processor 310, may use information about the user's activities todetermine the immediate networking connectivity performancerequirements, and determine an appropriate background scanning interval.Alternatively, or in addition, network usage application code module 315may inspect the network traffic of mobile station 110 in order to deduceits immediate networking connectivity performance requirements.Alternatively, WLAN controller 304 may itself inspect the networktraffic of mobile station 110 in order to deduce the immediate networkconnectivity performance requirements of mobile station 110 and toadjust the background scanning interval accordingly. If the method ofdirect monitoring of network traffic is used exclusively, network usageapplication 315 would be unnecessary, as the WLAN controller has theability to monitor traffic directly, and to control the backgroundscanning interval itself.

Processor 310 may be coupled to WLAN controller 304 and may be able tocontrol, at least in part, the operation of WLAN controller 304. Mobilestation 110 includes a battery 316 to provide power to radio 302, WLANcontroller 304, processor 310 and memories 306 and 312. Mobile station110 may include other components that, for clarity, are not shown.

Radio 302, WLAN controller 304, processor 310 and memories 306 and 312are functional blocks and may be implemented in any physical way inmobile station 110. For example, radio 302, WLAN controller 304,processor 310 and memories 306 and 312 may be implemented in separateintegrated circuits, and optionally in additional discrete components.Alternatively, some of the functional blocks may be grouped in oneintegrated circuit. Furthermore, the functional blocks may be parts ofapplication specific integrated circuits (ASIC), field programmable gatearrays (FPGA) or application specific standard products (ASSP).

A non-exhaustive list of examples for processor 310 includes a centralprocessing unit (CPU), a digital signal processor (DSP), a reducedinstruction set computer (RISC), a complex instruction set computer(CISC) and the like.

Memories 306 and 312 may be fixed in or removable from mobile station110. A non-exhaustive list of examples for memories 306 and 312 includesany combination of the following:

a) semiconductor devices such as registers, latches, read only memory(ROM), mask ROM, electrically erasable programmable read only memorydevices (EEPROM), flash memory devices, non-volatile random accessmemory devices (NVRAM), synchronous dynamic random access memory (SDRAM)devices, RAMBUS dynamic random access memory (RDRAM) devices, doubledata rate (DDR) memory devices, static random access memory (SRAM),universal serial bus (USB) removable memory, and the like;

b) optical devices, such as compact disk read only memory (CD ROM), andthe like; and

c) magnetic devices, such as a hard disk, a floppy disk, a magnetictape, and the like.

A non-exhaustive list of examples for antenna 300 includes a dipoleantenna, a monopole antenna, a multilayer ceramic antenna, a planarinverted-F antenna, a loop antenna, a shot antenna, a dual antenna, anomnidirectional antenna and any other suitable antenna.

Application code modules 314, when executed by processor 310, maymonitor current user activities. The network applications may sendinformation about the user's activities to another application thatdetermines an appropriate background scanning interval, or maythemselves determine a background scanning interval. Assigning a usagestatus mode such as described above may be performed as an intermediatestep to determining a background scanning interval. The backgroundscanning interval is then updated at WLAN controller 304, which controlsthe background scanning performed by radio 302.

Alternatively, mobile station 110 may periodically monitor its ownnetwork traffic in order to determine its current network access needsand an appropriate background scanning interval.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

1. A method for power management in a mobile station in a wireless localarea network, the method comprising: determining at different points intime different wireless network usage modes for the mobile station;determining at each of the different points in time a current backgroundscanning interval for the mobile station corresponding to the wirelessnetwork usage mode determined at that point in time; and ensuring thatfollowing each of the different points in time, any background scanningto check for neighboring access points is performed periodically at thecurrent background scanning interval until a different backgroundscanning interval has been determined.
 2. The method as claimed in claim1, wherein determining the different wireless network usage modescomprises: monitoring a user's activities at the application level. 3.The method as claimed in claim 1, wherein determining the differentwireless network usage modes comprises: monitoring the mobile station'snetwork traffic.
 4. The method as claimed in claim 1, whereindetermining the different wireless network usage modes comprises:monitoring which applications are active in the mobile station.
 5. Themethod as claimed in claim 3, further comprising: determining that thedifferent background scanning interval is shorter than the currentbackground scanning interval if the mobile station's network trafficincreases.
 6. The method as claimed in claim 3, further comprising:determining that the different background scanning interval is longerthan the current background scanning interval if the mobile station'snetwork traffic decreases.
 7. The method as claimed in claim 1, whereinthe different wireless network usage modes include at least two of thefollowing network usage modes: a mode in which the mobile station is notconnected to the network; a mode in which the only network activity ofthe mobile station is that which is required to maintain a connection tothe network; a mode in which the mobile station is connected to thenetwork and one or more applications that do not require a networkconnection are active; a mode in which the mobile station is connectedto the network and there is user interface activity at the mobilestation that does not require network resources; a mode in which themobile station is connected to the network and an email application ofthe mobile station is active; a mode in which the mobile station isconnected to the network and email is being sent by or received at themobile station via the network; a mode in which the mobile station isconnected to the network and an instant messaging application of themobile station is active; a mode in which the mobile station isconnected to the network and a network browsing application of themobile station is active; a mode in which the mobile station isconnected to the network and a media streaming application of the mobilestation is active; a mode in which the mobile station is connected tothe network and a media streaming session is in progress using a mediastreaming application of the mobile station; and a mode in which themobile station is connected to the network and a telephone applicationof the mobile station is active and a call is established via thenetwork.
 8. The method as claimed in claim 1, wherein the differentwireless network usage modes include at least two of the followingnetwork usage modes: a mode in which the mobile station is not connectedto the network; a mode in which the mobile station is connected to thenetwork with sporadic, intermittent network activity; a mode in whichthe mobile station is connected to the network with network activitycharacteristic of email transmission and reception; a mode in which themobile station is connected to the network with network activitycharacteristic of instant messaging; a mode in which the mobile stationis connected to the network with network activity characteristic ofbrowsing; a mode in which the mobile station is connected to the networkwith network activity characteristic of media streaming; and a mode inwhich the mobile station is connected to the network with networkactivity characteristic of telephone communications.
 9. A non-transitorycomputer-readable medium having computer-executable instructions thereonwhich, when executed by a processor of a mobile station, result in:determining at different points in time different wireless network usagemodes for the mobile station; determining at each of the differentpoints in time a current background scanning interval for the mobilestation corresponding to the wireless network usage mode determined atthat point in time; and ensuring that following each of the differentpoints in time, any background scanning to check for neighboring accesspoints is performed periodically at the current background scanninginterval until a different background scanning interval has beendetermined.
 10. The non-transitory computer-readable medium as claimedin claim 9, wherein determining the different wireless network usagemodes for the mobile station comprises monitoring which of the one ormore applications is active in the mobile station.
 11. Thenon-transitory computer-readable medium as claimed in claim 9, whereindetermining the different wireless network usage modes for the mobilestation comprises monitoring the mobile station's network traffic. 12.The non-transitory computer-readable medium as claimed in claim 11,wherein the different background scanning interval is determined to beshorter than the current background scanning interval if the mobilestation's network traffic has increased.
 13. The non-transitorycomputer-readable medium as claimed in claim 11, wherein the differentbackground scanning interval is determined to be longer than the currentbackground scanning interval if the mobile station's network traffic hasdecreased.
 14. A mobile station comprising: an antenna; a radio coupledto the antenna through which the mobile station is able to communicateover a wireless local area network; a wireless local area networkcontroller coupled to the radio, which is able to control a backgroundscanning process while the mobile station is associated to the network,the background scanning process occurring periodically according to anadjustable background scanning interval; a processor coupled to thewireless local area network controller; and a memory to store codewhich, when executed by the processor, is to determine at differentpoints in time different wireless network usage modes for the mobilestation, to determine at each of the different points in time a currentbackground scanning interval for the mobile station corresponding to thewireless network usage mode determined at that point in time, and toensure that following each of the different points in time, anybackground scanning to check for neighboring access points is performedperiodically at the current background scanning interval until adifferent background scanning interval has been determined.
 15. Themobile station as claimed in claim 14, further comprising: means formonitoring a user's activities at the application level.
 16. The mobilestation as claimed in claim 14, further comprising: means for monitoringthe mobile station's network traffic.
 17. The mobile station as claimedin claim 16, wherein the different background scanning interval isdetermined to be shorter than the current background scanning intervalif the mobile station's network traffic has increased.
 18. The mobilestation as claimed in claim 16, wherein the different backgroundscanning interval is determined to be longer than the current backgroundscanning interval if the mobile station's network traffic has decreased.19. The mobile station as claimed in claim 14, wherein the differentwireless network usage modes include at least two of the followingnetwork usage modes: a mode in which the mobile station is not connectedto the network; a mode in which the only network activity of the mobilestation is that which is required to maintain a connection to thenetwork; a mode in which the mobile station is connected to the networkand one or more applications that do not require a network connectionare active; a mode in which the mobile station is connected to thenetwork and there is user interface activity at the mobile station thatdoes not require network resources; a mode in which the mobile stationis connected to the network and an email application of the mobilestation is active; a mode in which the mobile station is connected tothe network and email is being sent by or received at the mobile stationvia the network; a mode in which the mobile station is connected to thenetwork and an instant messaging application of the mobile station isactive; a mode in which the mobile station is connected to the networkand a network browsing application of the mobile station is active; amode in which the mobile station is connected to the network and a mediastreaming application of the mobile station is active; a mode in whichthe mobile station is connected to the network and a media streamingsession is in progress using a media streaming application of the mobilestation; and a mode in which the mobile station is connected to thenetwork and a telephone application of the mobile station is active anda call is established via the network.
 20. The mobile station as claimedin claim 14, wherein the different wireless network usage modes includeat least two of the following network usage modes: a mode in which themobile station is not connected to the network; a mode in which themobile station is connected to the network with sporadic, intermittentnetwork activity; a mode in which the mobile station is connected to thenetwork with network activity characteristic of email transmission andreception; a mode in which the mobile station is connected to thenetwork with network activity characteristic of instant messaging; amode in which the mobile station is connected to the network withnetwork activity characteristic of browsing; and a mode in which themobile station is connected to the network with network activitycharacteristic of telephone communications and/or media streaming.